STUDY ON THE CONSTRAINT EFFECT USING THE DAMAGE MECHANICS APPROACH.

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(1) By changing the constraint condition, fracture toughness tests are conducted. The fracture toughness value, which is a macroscopic parameter, is affected by the constraint condition. By the observation of fracture surface using scanning electron microscope(SEM), it was shown that the microscopic parameter such as dimple diameter, dimple number and power value are also affected by the constraint condition largely.(2) The dimple fracture tests of notched specimen with different notch radius are conducted. The fracture surface observation showed that the stress triaxiality also affects the dimple fracture process strongly. The change of the stress triaxiality means the change of the constraint condition. Precise measurement of the dimple diameter and dimple aspect ratio is made, and more than 3000 data are obtained. It is base of the data-base on this research area.(3) The dimple fracture simulation is conducted using FEM considering the damage mechanics effect. Two kinds of tests described in (1) and (2) are simulated using this code. It is shown that the constraint effect was evaluated well. The effect of the non-uniform distributions of inclusions in the base matrix can be considered using this code. It became obvious that the non-uniform distribution of inclusions affects the dimple fracture pattern largely.(4) As a result, the relation between the constraint condition and the microscopic ductile fracture process is becoming clear, which is the basis of the study on the constraint condition from the microscopic fracture mechanics.